1. Technical Field
The present invention relates to an improved sheeter wire apparatus and, in particular, to a sheeter wire apparatus which provides for a continuous advancement of sheeter wire using a simple design that provides constant tension on the feed spool even during wire breakage. This is accomplished by the use of a drag motor connected to the supply spool, a constant speed motor connected the take-up spool, and a feed spool tension device.
2. Description of Related Art
A sheeter is a device commonly used in the food industry for making flattened food products, such as tortilla chips, in a continuous processing operation. Typically, a dough product is compressed between a pair of counter rotating sheeter rollers that are located closely together, thereby providing a pinch point through which the dough is formed into sheets. The dough can then be cut by, for example, a cutting roller to form the shape of the product desired.
Many dough products, particularly those that are corn based ("masa"), have a tendency to stick to the sheeter rollers rather than dropping onto a conveyer for transportation to the next processing step, such as a baking oven. One common approach to this problem is to string a stripper wire across the face of the sheeter roller so that the stripper wire can scrap away the dough product off of the surface of the roller.
An example of a prior art design in this regard is illustrated by FIG. 1. FIG. 1 is a perspective view of the output of a dough sheeter device 110. The cut dough product, in this case uncooked tortilla chips 120 made from masa, can be seen on a conveyer 130 after being deposited on the conveyer 130 by a sheeter roller 140. The sheeter roller 140 will typically have plurality of plastic bands 150 about the circumference of the sheeter roller 140. These bands 150 ride in groves (now shown) in the sheeter roller 140 and hold the sheeter wire 160 close to the surface of the sheeter roller 140. The bands 150 also provide a surface for returning ribbons of unused masa to the sheeter 110. A sheeter wire 160 is shown strung across the face of the sheeter roller 140. This sheeter wire 160 is attached to two fixed points 170, 180 and is threaded across the face of the sheeter roller 140 underneath each of the bands 150. This provides a flush contact between the sheeter wire 160 and the surface of the sheeter roller 140.
Also shown is a tension device 190, which can be a hydraulic or pneumatic device that provides a constant tension on the wire 160. This tension device 190 is typically connected to a warning device to provide an indication of wire breakage. Alternatively, the tension device 190 can also act as the second fixed point, thereby eliminating the post 180 shown in FIG. 1. FIG. 1 shows the sheeter wire 160 on the front or open side of the sheeter roller 140. The sheeter wire 160 can also be located in the same relative vertical position but on the back, or concealed, side of the roller 140.
The sheeter wire 160 is typically commercial piano wire. A typical tension on the wire during operation is 100 to 125 pounds. Contact with hardened masa, particularly during start-up, can subject the sheeter wire 160 to higher tension for short time periods. During operation the wire is also subject to friction from the moving face of the sheeter roller 140. The wire 160 must be replaced periodically or it is prone to breakage after time. In fact, in a continuous use operation for a typical sheeter device producing tortilla chips, it has been observed that such fixed sheeter wire 160 will break, if not replaced, nearly daily.
In order to replace a broken sheeter wire 160 the entire sheeter device 110 and, consequently, the entire chip processing assembly, must be stopped. The old sheeter wire 160 is removed. A new sheeter wire 160 is attached to the first attaching point 170, strung across the face of the sheeter roller 140 under the bands 150, and attached to a second attaching point 180. Then the tension device 190 must be reactivated. Raw material is lost because the dough that was on the sheeter must be thrown away and additional product downstream my need to be discarded. In addition, line start-up procedures must be initiated, which usually results in the loss of further product. A wire breakage event, therefore, results in a substantial amount of unscheduled downtime and lost product. The alternative is to schedule, on a daily basis, the replacement of the sheeter wire 160. A scheduled replacement of the sheeter wire 160, however, results in even more frequent, although scheduled, downtime.
One attempt at addressing the wire breakage problem is reflected in U.S. Pat. No. 5,720,990 ("Lawrence") issued on Feb. 24, 1998. The Lawrence patent discloses a wire separator system for a sheeter device comprising a motor that drives a feed spool and a motor that drives a take-up spool. Tension is maintained on the sheeter wire by use of a tension sensing pulley providing input to a controller which modulates the torque on the take-up reel. Provided that the wire does not unexpectedly break, the Lawrence patent discloses a device that will allow the sheeter to run for long periods of time without the necessity of stopping the sheeter to replace the sheeter wire, because new wire is constantly drawn across the contact surface.
The invention disclosed by Lawrence has several drawbacks, however. First, the design assumes that the wire will not break during operation. Unfortunately, this is not a safe assumption. In fact, it is not an infrequent occurrence that wire breakage occurs on the prior art model illustrated by FIG. 1 shortly after a new wire has been installed. This could occur due to a sudden contact with a dried piece of dough that has become affixed to the sheeter while the sheeter is stationary. Further, an initial steady-state friction between the sheeter wire and the sheeter must be overcome at the instant the sheeter begins to rotate. Since the Lawrence device provides that one motor feeds wire while another motor takes-up wire, a breakage between the two motors can result in the continued feeding of wire into the sheeter until the feed motor comes to a stop. A breakage also results in a loss of tension on the feed spool and can lead to unraveling or the "weed eater" effect, whereby the spool becomes unwound. Further, the Lawrence device is designed to maintain constant tension of the wire by using a variable speed pulling motor connected to the take-up reel. Since the Lawrence feed spool is connected to a fixed speed motor, the tension will necessarily fluctuate at the point that the wire is leaving the feed spool when, for example, the wire encounters a piece of dried dough product on the sheeter during operation. These torque fluctuations could effect the consistency of the feed spool's wound tension, thereby leading to further torque fluctuations and potential feed problems.
Consequently, a need exists for an improved continuous sheeter wire apparatus that maintains a constant tension on the feed spool even during wire breakage. This apparatus should be designed, in a fail safe way, to avoid driving sheeter wire into the sheeter after a wire breakage. The improved apparatus should also be of a relatively simple design with a minimum number of necessary and washable components.